1. Field of the Invention
The present invention relates to shoe construction. More specifically, the present invention relates to methods and apparatus for a dynamic dual density heel bag for use in athletic and walking type shoes to provide cushioning and shock absorption to the foot to enhance comfort and support, security and stability to the foot for avoiding sprained ankles.
2. Description of the Related Art
The relevant art is directed to means and methods of constructing footwear to improve the comfort to the human foot. Much effort has been expended in designing sole and heel shoe components which are comfortable yet robust exhibiting a tough construction which yields to the movements of the human foot.
In one example, a method to manufacture a welted article of footwear is disclosed in which a shaped board is temporarily secured to one side of a flexible insole prior to the securing of a lasted upper to the insole. The flexible insole is formed with extended marginal portions which in the finished article of footwear extend up the sides of the upper so as to cradle the foot. The welted article of footwear also includes a cushioning structure comprising a rib member made of a rubbery material which surrounds a resilient filling of sponge rubber. The rib member surrounds or bounds the sponge rubber filling but does not cradle it.
In another example, a shoe has a shock-absorbing structure comprising a hydrodynamic pad positioned within the midsole of the shoe. The hydrodynamic pad includes inner and outer fluid-filled bladders which are interconnected by fluid channels and configured such that displacement of fluid from the center of pressure distribution generated by foot impact radiates from the inner bladder outwardly to the outer bladder through the fluid channels. This action causes the outer bladder to expand for seating the heel of the foot. The hydrodynamic pad cushions and stabilizes the foot by a controlled displacement of fluid between the inner bladder and the outer bladder which are located in the same plane and are interconnected to pass a fluid of constant density. Pressure applied to the inner bladder by the foot forces constant density fluid through the channels to the outer bladder. The outer bladder is positioned outwardly from the inner bladder, i.e., the pair of bladders are not vertically stacked and are not isolated from one another.
Another example teaches a sandal with a soft sole body formed of non-rigid plastic material having a relatively hard non-foamy surface layer with soft pliable surface inside. The sole is provided with a plurality of recesses used for air distribution to a foot. A reinforcing plate, which serves as an insole, is formed of rigid polyvinylchloride (PVC) plastic material having a suitable thickness to prevent flexion on the rear half. Thus, the top layer is the reinforcing plate comprised of rigid PVC and the bottom layer is the sole comprised of non-rigid plastic with a soft pliable surface inside.
A further example teaches a resilient member adapted for use within the sole of an article of footwear and buried within multiple layers of a polyurethane foam positioned over the full length and width of the sole. Materials other than polyurethane foam can be used as long as the substitute material is sufficiently hard to provide adequate shock absorption and soft enough to provide sufficient cushioning and comfort. Windows are included in the footwear to enable the resilient material to be viewed from the exterior of the shoe. A main feature in this example is a resilient member, the function once compressed by the foot is to quickly return substantially to its unstressed position to return substantial amounts of energy to the foot quicker than could be provided by polyurethane foam. The cradling effect of an upper layer of polyurethane foam is the result of the vertical portions of the resilient member and the cradle element.
Several problems associated with the foregoing footwear designs include multiple bladders which are located in the same plane and use fluids of constant density. Consequently, the two bladders will function with the same parameters instead of one bladder serving as a cushioning medium and a second bladder located in another plane serving as a stabilizing medium. Additionally, multiple bladders located in the same plane necessarily require that the bladders be smaller (than vertically-stacked bladders) and thus less effective. In constructions which utilize sponge rubber, adequate cushioning is not realized. Further, in cases which utilize multiple interconnected bladders, use of fluids of different densities is not possible.
Thus, there is a need in the art for a dynamic dual density heel bag for use in shoe construction that includes a lower sealed enclosure which contains a stiff dynamic high density material for providing support and stability to a foot, a separate upper sealed enclosure which contains a shock-absorbing low density material for providing cushioning to the foot, where the upper enclosure is cradled by and sealed to the lower enclosure to form the heel bag that is affixed within the outsole of a footwear.